In general, a GaN-based light-emitting diode (hereinafter abbreviated as “LED”) is composed of a semiconductor multilayer film obtained by crystal-growing a III-V group nitride semiconductor, represented by the general formula BzAlxGa1-x-y-zInyN1-v-wAsvPw (0≦x≦1, 0≦y≦1, 0≦z≦1, 0≦x+y+z≦1, 0≦v≦1, 0≦w≦1, 0≦v+w≦1), on a single crystal substrate such as a sapphire substrate. By feeding a current through this semiconductor multilayer film, wide range of light from an ultraviolet region to an infrared region (e.g., 200 to 1700 nm) can be emitted therefrom. Especially, a LED emitting light in a wavelength region shorter than a blue-green region currently is developed eagerly.
Above all, a blue LED emitting blue light can be combined with phosphors emitting yellow light and red light by the excitation of the blue light, so as to be utilized as a white LED emitting white light. The white LED can realize a longer life as compared with an incandescent lamp and a halogen lamp, and therefore the white LED is a prospective substitute for currently-existing light sources. Alternatively, by combining several kinds of LEDs emitting ultraviolet light and near ultraviolet light with a phosphor emitting fluorescence in a wavelength region longer than blue, a white LED can be configured as well.
However, while general incandescent lamps (60 W) have a luminous flux of about 800 lm, a white LED adopting a 1 mm square of blue LED bare-chip has a luminous flux of about 30 to 60 lm. Therefore, in order to use a white LED as an illumination light source, a higher luminous flux has to be achieved. To this end, a module with a large number of white LEDs integrated therein is proposed by JP 2003-124528 A, for example. In the module proposed by JP 2003-124528 A, the white LEDs are flip-chip mounted on a mounting board without submount boards intervening therebetween. According to this mounting technology, the mounting area can be equal to the chip size, and therefore high-density mounting is enabled and a large number of white LEDs can be mounted in the mounting board having a limited size. As a result, a high luminous flux light can be obtained from the module. The module proposed by JP 2003-124528 A, however, has the following problem: since a large number of white LEDs are flip-chip mounted on the mounting board, a failure in mounting of one white LED directly leads to a defective module, thus making it difficult to improve the yield.
On the other hand, JP 2001-15817 A for example proposes a module with a large number of white LEDs mounted on a mounting board with a submount board intervening therebetween. In this module, a blue LED is flip-chip mounted on the submount board, followed by the formation of a phosphor layer on the submount board so as to cover the blue LED, whereby a semiconductor light-emitting device including a white LED is formed, and then this light-emitting device is mounted on the mounting board. Thus, the semiconductor light-emitting device can undergo the inspections of electrical or optical properties before the mounting on the mounting board, and therefore non-defective semiconductor light-emitting devices alone can be selected and mounted on the mounting board. Thereby, the yield can be improved while minimizing waste for the manufacturing process of the module.
The module proposed by JP 2001-15817 A, however, has a difficulty in densely mounting the white LEDs. Therefore, there is a possibility of a shortage in luminous flux of the light obtained from the module. Further, since the phosphor layer is formed in a substantially rectangular parallelepiped shape, the light extracted from the module has anisotropy, and therefore the extracted light may have non-uniformity in color.